Certain types of prior personal computer systems each include a microprocessor (also referred to as a central processing unit or CPU) that is coupled to several types of storage systems--namely, a read only memory ("ROM"), a random access memory ("RAM") or dynamic random access memory ("DRAM"), a hard (i.e., fixed) disk drive for mass storage, and a floppy disk drive or drives for storage on removable magnetic floppy disks. The floppy disks are also referred to as diskettes.
A relatively new prior mass storage device is a flash memory card. One prior art flash memory card includes flash electrically erasable programmable read only memories ("flash EPROMs") and an electrical connector as part of a plastic package that is smaller than a 3.5 inch floppy disk. The flash memory card can be connected to a personal computer via the electrical connector.
The flash EPROM is a nonvolatile memory that can be programmed by the user. Once programmed, the flash EPROM retains its data until erased. Electrical erasure of the flash EPROM erases the entire contents of the memory of the device in one relatively rapid operation. The flash EPROM may then be reprogrammed.
That prior flash memory card allows for the storage of data files and application programs on the purely solid-state medium of flash EPROMs. System resident flash filing systems permit the prior flash memory card to function as if it were a physical disk drive. A prior flash memory card in conjunction with a flash filing system provides an alternative to both a fixed hard disk and a floppy disk in a Disk Operating System ("DOS") compatible portable personal computer ("PC").
The storage of user application software on a prior flash memory card substantially reduces the relatively slow prior disk-DRAM download process. That prior flash memory card can be read from faster than certain prior hard disk drives. That prior flash memory card generally uses less power than certain prior hard disk drives. That prior flash memory card is also smaller and lighter than certain prior hard disk drives.
Prior personal computers typically have a redundant memory structure--i.e., there is a DRAM for storage of applications and data to be executed plus a hard disk or a floppy disk for mass storage. Applications and data need to be loaded into the DRAM.
The prior flash memory card, however, has a read access time and a command register microprocessor write interface that permits an "execute-in-place" architecture. This configuration eliminates the need for a DRAM. Thus, redundancy associated with having both a DRAM and disk drive is eliminated.
Certain prior flash memory cards can be transported from personal computer to personal computer. Moreover, the flash EPROMs of certain prior flash memory cards are nonvolatile and thus do not require a battery back-up.
One type of prior flash EPROM used in a prior flash memory card has a standby mode that disables most of the flash EPROM circuitry and reduces device power consumption. The prior flash EPROM also has an active mode. The active mode requires increased power consumption. The active mode is used when the flash EPROM is being written to, read from, or erased.
One disadvantage, however, of certain prior flash memory cards is that a microprocessor has to step through relatively complex erasure or programming software routines in order to erase or program the flash memory card.
Another disadvantage of certain prior flash memory cards is that even when the flash EPROMs making up the card are in the standby mode, the flash memory card still consumes a significant amount of power. The amount of power consumed by a flash memory card with flash EPROMs in the standby mode is especially noticeable when the flash memory card is used in conjunction with a battery-powered laptop personal computer. In order to extend battery life, power consumption must be kept to a minimum for a battery-powered laptop personal computer.
Recently, improvements have been made in prior flash EPROMs. Memory capacity has been increased. In addition, one type of prior flash EPROM includes a write state machine on the flash EPROM chip.
The write state machine comprises circuitry that automatically steps the flash EPROM through a multistep program or erasure sequence upon receiving an initiating command from a microprocessor. The flash EPROM includes a ready/busy output pin that indicates whether the write state machine is ready to accept a command or whether the write state machine is currently busy programming or erasing the flash EPROM.
That type of prior flash EPROM also includes a power down mode that can be initiated by applying a logical signal to a power down pin. In the power down mode, the flash EPROM consumes less power than in the standby mode.